Diamond grinding wheel construction



May 25, 1948.

G. E. HOLLSTROM DIAMOND GRINDING WHEEL CONSTRUCTION Filed Aug. 6, 1945 E. HDLLSTRUM GHUNNAR Patented May 25, 1948 UNITED- STATES Y PATENT OFFICE v DIAMOND GRINDING wager, CONSTRUCTION I (.lunnar E. Hollstrom, Worcester, Mass., assignorto Norton Company, Worcester, Mass, a corporation of Massachusetts Application August 6, 1945 Serial No. 809,202 2 Claims. (01.51-209) This invention relates to grinding wheel or grinding disk construction, and more particularly to grinding disks for surface grinding-usually flat surfaces of various materials, such as glass.

One of the objects of this invention is to provide a practical and efllcient grinding disk construction that will be of relatively inexpensive, yet strong and durable, construction and well adapted for eiiicient use of costly abrasives, such as diam'ond grains, diamond dust, and the like. Another object is to provide a built-up abrasive structure of the above-mentioned character in which the individual parts will 'be capable of efficient and inexpensive manufacture and rapid and dependable assembly. Another object is to provide an abrasive structure of the just-mentioned character in which diamond or like abrasive-bearing elements can be reliably mounted in position to effectively withstand the thrusts and stresses of grinding reaction. Another object is to carry out the last-mentioned object in a manner to achieve ease and speed of replacement of such elements without impairment of reliability and efficiency of support or mounting. Another object is to provide a multiple or built-up structure of the above-mentioned character with means to expeditereplacement of [elements of the just-mentioned character. Another object is, in general, to provide an improved disk 'type of abrasive structure, particularly for the grinding of surfaces of large areas, usually flat, and other objects will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements, and arrangements of parts as will be exemplified in the structure to be hereinafter described and the scope of the application of which will be indicatedin the' following claims.

In the accompanying drawings, in which are shown several of the various possible embodiments of my invention- 1 V,

Fig. 1 is a plan view of a ring or disk type of abrasive structure made according to my invenof certain of the materials that may be employed.

Similar reference characters refer to similarparts throughout the several views of the drawings.

Referring first to Fig. 1, I have there shown a disk-like or annular support, generally indicated by the reference character l0, preferably provided with an internal or central opening II for a purpose later described and projecting from its front face II which, illustratively, is flat or plane, is a suitable number of suitably distributed individual or separate and preferably composite or built-up elements, generally indicated by the reference character E, each constructed to have a cantilever portion and to present at the outer end 'of the cantilever part an abrasive face l5a of any suitable shape or. configuration, illustratively circular.

20 port In and where the grinding operation is to be performed upon a fiat surface such as plate glass, for example, the faces [5a fall in the same flat plane though it is to be understood that, according to the particular grinding operation to be performed or the shape of the surface of the workpiece to be ground, the abrasive faces iia can be shaped to define or fall within any other suitable surface of revolution.

Any suitable and preferably uniform distribution of the elements E throughout the face l2 of the support l0 may be used and in the drawing I have shown a uniform distribution achieved by positioning the elements E at equal distances fromxthe axis of. the support iii and giving them equal spacings, center to center, along the geometric circle on which their centers thus lie.

The annular support In is adapted to be mounted in any suitable way for rotation at suitable speed-illustratively, about a vertical axiswith the elements E on the underside of the support i0, and any suitable means (not shown) may be employed for so mounting and driving the support l0; usually such means are constructed to be provided with a suitable passage or passages, usually coaxial, for guiding a suitable liquid c001- ant to the area of the work-piece that falls within the effective abrasive annulus as the abrasive structure is pressed against the surface of the work-piece being ground, whence it moves or flows radially outwardly to be brought into the region of grinding contact with the workpiece. In Fig. 1 I have indicated at H a number of suitably distributed, threaded holes opening from the underface of the support III. as viewed in Fig. 1,

I 66. and being of suitable depth, whereby, with the The cantilever abrasive-carrying elements 'E project beyond the face I! of the annular supa a eyes use of screws, the annular support I is secured to any suitable driving carrier such as the kind just described. These holes |3 need not emerge at the face '|2 of the support Ill, and they can be proportioned or located so as not to interfere with the location, mounting, or construction of the elements E.

For convenience of illustration, as well as convenience of manufacture of the construction, the elements E are preferably of circular cross-sectionparticularly as to the mounting portion thereof, as later described--though it will be understood that my invention is not thereby to be so limited excepting as it may be so limited in one or more of the claims. Each element preferably comprises an abrasive portion l5 and a mounting portion l6, and preferably and conveniently these two portions are of the same cross-section, illustratively circular, and they may be initially formed as a single entity or unit, or they may be separately constructed and then integrally joined or united. In axial-length, that is, in their dimension parallel to the axis of the annular support I0, the mounting portions l6 of the elements E are preferably of substan tial length for coaction' with the annular support III, in a manner later described, and they are constructed to have good resistance against strain in a direction transversely of their length; a circular cross-section is illustrated in the drawings and is good for this purpose. Referring to Fig. 2, the support I0 is preferably of substantial vertical or axial dimension and, opening into the annular face l2 thereof, it is provided, in any suitable way, with receiving chambers C, one for each element E, each preferably of substantial depth or axial dimension. The mounting portion |6.of the element E and the chamber C are of .similar cross-section, illustratively circular, and the two parts are proportioned sothat the one is receivable into the other with the desired fit which may be tight or snug or may have some tolerance according to clrcumstanceslater described.

. In the form shown in Fig. 2, the mounting portion l6 of element E is a straight cylinder as is also the wall H of the chamber C, and preferably the end face l8 of the element E extends at right angles to the axis of the element, in which 'case also it is preferred that the bottom wall IQ of the chamber 0 extend likewise at right angles to its axis so that the face l8 and the wall l9 can be parallel to each other.

Preferably coaxially of each chamber C, I provide a hole 2| in the annular support III, which hole is threaded, as shown, being preferably of a diameter relatively large as compared to the diameter of the chamber C, and hence, where face of the support "l0, being accommodated in a counterbore 21 which is of such a depth as to permit the end of the screw, when it is turned.

to partake of substantial movement into the' chamber C, the counterbore 21. being of sufficiently large width to accommodate a socket wrench or the like when applied to the screw head 24 to 'turn it. Any suitable pitch of thread may be employed, and preferably a thread of relatively small pitch, so that, upon turning of the screw 22, its axial movement is relatively small per unit of angle of turn so that substantial multiplication of force may be achieved, for purposes later described. With the screw 22-24 normally accommodated within the plane of the face ,2lof the annular support "I. the latter may be secured to the rotating or driving carrier above described without interference by or from the screw head 24, and in Fig. 2 I have indicated.

in broken lines at 29, such a driving carrier against a face of which the face 25 of the annular support l0 rests and is clamped, as by the above-mentioned screws coacting with the holes '|3 in the support I'D, thus also closing over the I cross-section, they may be formed in a similar manner. Or the annular support l0 may be formed of any other suitable material, such as moldable and usually heat-curable material, usually resinous in character, and including any suitable fillers or other ingredients or materials to give 'it the desired characteristics. case the annular support It) may be molded in a suitable mold, by known techniques, usually employing pressure andheat during the vmoldmolded and heat-treated. In such case the the hole 2| is employed, the bottom wall of the that with the annular wall I! it can form a com plete bottom 'wali for the chamber C. The screw 22 is provided with any suitable means to facilitate' turning it, and conveniently this takes the form of a head- 24, which may be hexagonal. Preferably also the cross-section of the annular support III is so proportioned and dimensioned that, with the end face 23 of the screw 22 in' alignment with the bottom wall IO-of the chamber C, the head 24 falls within the annular end is the same as is used, according to my invention,

holes 2| are molded straight and are threaded after cure. In any case the support I0 is made of a material that will give the desired rigidity of support to the cantilever portions of the elements E; its U-shaped cross-section can advan tageously coact in this respect.

The elements E preferably have an abrasive portion l5 and a mounting portion l6, as above described, the abrasive portion l5 preferably having diamond grain or powder as the abrasive mgredient-in which case the axial dimension or thickness of the abrasive portion l5, as viewed in Fig. 2, may be relatively small-on the order of {6", 8",.or the like-bonded by any suitable bondin'gmaterial, and preferably a material that in making the mounting portion l6. For exam ple, I may use'any material known in the art as resinoid"--andof which phenol formaldehyde In such inbnd grain in making up the abrasive portion II and as the material, with or without suitable fillers, which to make the mounting portion ll. For example, for the latter I may include powdered metal-illustratively, in the proportions above mentioned-and, depending upon grinding characteristics desired for the abrasive portion Ii,

I may also include in the latter any suitable metal in powdered form. The portions to and it may have their respective ingredients first suitably mixed in two respective mixes and then suitable quantities of these two mixes successively placed in a suitable mold, which is preferably shaped to give theabrasive portion a rounded-over annular portion R of suitable radius, somewhat as indicated in the drawings, for a purpose later described. The two mixes in the mold arethen subjected to suitable pressure and, if desired, one mix, such as that of the abrasive portion. i5, may first be injected into the mold and subjected to pressure, andthereafter the mix representing the mounting portion i6 superimposed and again pressure applied, whence curing, as by heat, takes place. The two portions are thus strongly. united along a plane of demarkation, indicated at P, and the iunction at P in this preferred manner is given a character such that shear in the direction of the plane of the junction, under the stresses of grinding, is adequately withstood.

Instead of employing a resinoid material which includes rubber, both natural and synthetic, I may employ other materials, such as vitriflable mixes or bonds, molding or forming them and lip ingthem in known manner. The portions 15 and I. in such case, are preferably assembled or molded as a unit, so that the vitrifiable bond materials of the two portions unite along the plane at the Junction P to form an integral abrasive element E. Or I may form or make the portions i and lb of the abrasive element E separately 01 any suitable materials or combinations of materials, and unite the abrasive portion i5 and the mounting portion is along the plane P by the use of any suitable cementing or joining material, such as resin cements which are self-curing or self-setting, or resin cements that can be set. or cured under suitable heat treatment.

For example, the latter maybe of solid metal throughout and so, also, the mounting portion! 86 to which the wafer-like abrasive portion i5 is integrally united in a manner such as that just described. Such an arrangement makes it possible to match the thermal coefiiclents Of expansion of the mounting portion i6 and the annular support it, and permits the economical application of abrasive portions or wafers i5 according to whatever bonding material for the diamond grain is most suitable or desirable for the particular grinding task. Where the mounting portion is molded, with or without the abrasive portion to, the mounting portion to may be, with facility, given the desired dimensions for coaction with the chamber C-though, if desired, these parts I, may be molded somewhat oversize and then turned or ground down to the desired dimension for coactlon with the chamber 0.

In one form or my invention the mounting portion it oi the abrasive element It is dimensioned to be received in the chamber 6 with a very slisht clearance between the side walls to accommodate therebetween'a suitable cement or settable adhesive-for example, a cement of the kind described above in case the abrasive portion I! and the mounting portion is are cemented togetherand a clearance on the order of one or twothousandths of an inch or so, varying with the cross-sectional dimensions or the part I! and the chamber 0, may suflice. In seating the mounting portion I8 in the chamber C, the adhesive or cementing material, in suitable liquid or semiliquld form, is applied to the side and bottom walls or the chamber C and to the side and bottom faces of the mounting portion 16, and the latter then forced or pressed into the chamber C. This is preferably carried on with the screw 22 removed, particularly in cases where it is desired to maintain minimum possible clearance, the hole at thus preventing entrapment of air and the creation of possible voids in the layer or iilm of cement, as might be the case if the c amber C were closedat its bottom so that th' entry of the mounting portion i8 would have a piston action; such piston action, in compressing the air ahead or the part II as it enters the chamber- C, can have the eiIect of blowing more or less of the cementing material out through the side clearance as the air seeks escape. with my invention, however, a dependable and uniformly distributed layer of the cementing material or the desired thickness may be dependably achieved, it being noted that the chamber C is of substantial depth toreceive a substantial length of the mounting portion it to give the latter good lateral or transverse mechanical support against the reaction from the grinding stresses. That reaction is one of transverse shear as viewed in Fig. 2, tending to bend the mounting portion i6, and it increases with increase in the pressure of the rotating grinding unit (upwardly in Fig. 2) against the surface of the work being ground which is engaged by the upper end face i5 of the abrasive portion in; as against such stresses,

the relationship between the chambers (l and mounting portions 56 gives good rigidity of support against displacement and also dependable cantilever anchorage for the mounting portions it so that they cannot tilt or vibrate or chatter. With uniformly-dimensioned abrasive elements E, the arrangement above described also iacilitates the uniform bottoming or all of the composite elements E against the bottom walls it of the chambers C, thus bringing all of the abrasive faces th of the abrasive wafers substantially into the same plane and thus lessening the extent, if any, to which these end faces it need to be sub: sequently ground oil or trued to place them in the desired common plane.

The cement may now be allowed to set, or the structure may be heat-treated where the cement requires heat to cure it, whereupon the screw 22, preferably with cement applied to its end face 23, may now be entered into the threaded hole it to a position substantially like that shown in Fig. 2, thus closing oil the hole 2! and interposing a layer of him of settable or curabl cement between its end fac 23 and the central portion of the end face 88 of the mounting portion IE; or the screw 22 may be so entered into position before the cement that joins the mounting Portion ii of the walls of the chamber C is set, particularly it heat treatment is rmuired, so

that subsequent heat treatment effects setting of that cement, as well as the cement at the end face 23 of the screw 22.

The driving or supporting carrier 29 may now have the grinding structure applied to it and the end .faces Ill may be trued, if needed, it being noted that a minimum loss, if any, of expensive abrasive, such as diamond grain, is incurred due to the features of achieving nicety of alignment above described. In operation the roundedover portions R of the abrasive portions l form, with the surface being ground, an appropriate angle to facilitate entry into the grinding contact between the work and the abrasive portions.

of liquid coolants or grinding-promoting liquids, and the number and distribution of the abrasive elements E facilitate bringing to these angles of the liquid or liquids desired, the spacings between the elements permitting free flow of the liquids between the abrasive portions II, as earlier above indicated. Substantial pressures, as may be needed, may be exerted between the rotating grinding structure and work, and the side or lateral thrusts are well resisted, in shear,

by the projecting part of the mounting portion i6 and transmitted and taken up by the annular support it) without tilting of the mounting portion l6 relative to the axis of the annular support i0.

When the diamond-bearing abrasive portion I! of each of the composite elements E is worn down to the plane of junction P, the annular support I0 is detached from the carrier 29 for wall I! of the chamber C are threaded, prefer ably throughout .the entire length of the chamber C, and this arrangement is particularl feasible where the securing portions IQ of the elements E are made round in cross-section, In

such caseI preferably again employ ahole 2|.

, suitable known lever arrangement, the tool being replacement of the worn elements E, This is achieved by applying a socket wrench to the head 24 of the screw 23 and turning the screw, with appropriate leverage, to thread ,or move it upwardly as viewed in Fig. 2. The torque thus applied to'turn the end face 23 of the screw 22 breaks, as by shear, the cement uniting the end face of the mounting portion l6 to-the screw and through the upward movement of the screw 22, there is applied to the element E a force which is a very substantial multiplication of'the force applied to the socket wrench to dislodge the element E from its chamber C and, where cement is employed as above described, to break the union or junction efiected by the cement. In the illustrative embodiment in-Fig. 2, the bond of the cement between the-side face of the mounting portion I 6 and the side wall I! of the chamber C is broken as is also the Junction between the annular bottom wall l8 and the contiguous portion of the bottom face 23 of the element E.

By using a thread of small pitch, the force exerted by'the screw 22 to dislodge the inserted member can be made of appropriate magnitude.

' The elements E may thus be quickly removed.

The walls of the chambers C are suitably cleaned of! of any remnants of cement adhering thereto, whence new elements E may be assembled to the structure in the manner above described. 'F'urthermore, I may secure the cantilever mounting portion l6 in its chamber C by the frictional grip of the side walls of the latter upon the side surfaces oi the former, and such an anchorage may be effected by apressure or force fit of the one part in the other; such an anchorage is best effected where both parts are metallic, but I do not mean thereby so to limit my invention. With such an anchorage replacement of elements E is easily effected in the manner above described by the use of the screw 22.

In Fig. 3 suitable lengths of the mounting portion 18 of the abrasive element E and of the side interengageable with the lower end of the mounting portion l8 by way of the hole 2|. Preferably the hole 2| is threaded as shown in Fig. 2 to receive screw 22; after the element E is tightly threaded into the chamber C, preferably so that a suitable shoulder "or face such as its underface' l8 bottoms against the annular shoulder orwall IQ of the chamber 0, the screw 22 may be turned up to bring its underface 23 flatwise into engagement with the underface l8. oi the element E and serve as a Jamming or locking screw to resist loosening up or turning of the abrasive element E, particularly under the vibration or stress of grinding. I

The screw 22 may be provided with a head 24 which, as in Fig. 2. may be accommodated in a counterbore 21 of the annular support iii. If desired, a suitable cement-such as any of those set forth above-may be employed to coact between the mounting portion l6 and the chamber C and between the mounting portion l6 and the end face 23 of the screw 22. Forexample, cement may be applied between the end face ii of the element E and the annular bottom wall IQ of the chamber 0 and the end face 23 of the screw 22, and, when set, aids in holding the parts in position and in resisting relative rotary movement between the element E and the screw 22. If desired, also, a thin coating of thin cement may bev applied to the interengaged threaded portions of the mounting portion l6 and the chamber C, particularly if the mounting portion i6 is made ofa material that does not lend itself to the formation therein or thereon of accurate threads to match the, accuracy of the threads with which the walls of the chamber C may be provided-as by tapping. In such case the cement serves not only as a dependable joining or securing medium, but also, in filling the spaces left by any irregularities in the otherwise mating threaded portions, gives the mounting more dependably the advantages of strength, rigidity, and security of a tightly lnterflttedthreaded joint.

Replacement of the elements E in Fig. 3 is greatly facilitated. If a cement is employed, the cemented joints may be initially weakened or broken by aninitial slight turning movement apis simply backed off and out of the threaded hole 2 I, and thereafter the element E unthreaded'from the chamber C.

Referring now to Fig. 4. I construct the cantilever mounting portion l8 of the abrasive element so that it may function when seated in the chamber C as one of two clamping elements which, in coaction with a suitable connecting tension .element, can serve to clamp between them a suitable portion of the annular support I0.

Thus I provide a tension member 3|, for example,

of round cross-section and of steel, to pass freely through the threaded hole 2| with which its unthreaded shank preferably snugly interfits, and

provide it at one end with a head 32 to serve as the other clamping elementwhich can engage throughout a suitably large area with the annular bottom face 21" of the counterbore 21; at its other end the tension member M is threaded for threaded engagement with the mounting portion It which, in this illustrative embodiment, in effect functions as a nut. Thus the mounting portion I6 is provided with a threaded hole It opening at its bottom end face 23,, being preferably of substantial extent or depth, preferably along the axis of the element E where the latter is of circular cross-section and where only one tension element is to be employed.

I The element E, with or without cement applied to its mounting portion and to the walls of the chamber C, may thus be tightly drawn into the chamber C by operation of the companion clamping element at ,the other end of the tension rod 3|, such as the head 32 integrally formed therewith and suitably shaped, for example, hexagonally, so that it may be engaged by a suitable tool, such as a. socket wrench, and turned to cause the head 32 and the element E, through the mounting portion l8 thereof, tightly to clamp the annular support it) therebetween. Here also, if desired, the mounting portion I G of the element E may be pressure or force-fitted into position; in such case the headed tension member 3i may thereafter be applied and put under tension, in eflect locking the anchorage against loosening up.

When replacement is necessary, the part 3 I --3'2 is unthreaded from the threaded hole lii in the mounting portion it, whence a screw, like the screw 22 of Fig. 2 or 3, is then threaded into the threaded hole 2! to dislodge the element E from the chamber and, if a cement is employed, to break the union or junction effected by the cement. 7

Where the tension elementti is threaded into the element E, the mounting portion it of the latter is preferably made of a material such as metal, resinoid, powdered metal, resin-bonded powdered metal, hard rubber, or like materials that are better adapted for the formation of threads therein and to take the strain, particularly where the element E is set inthe chamber without the use of a cement or the like and the clamping action is relied upon to retain it in place. However, many of the advantages of my invention may be achieved with the use of materials less well'adapted for threading and taking a substantial strain on the threads, for in such case a cement or like substance is preferably employed on the walls of the chamber C, the threaded arrangement and tension member sufficing to draw the element E dependably into position within the chamber C for subsequent setting of the cement'or like securing material. Moreover, with materials less well adapted for direct interengagement threadedly with the threaded tension element 3 l such as ceramically or vitrified-bonded materials, resinoid, hard rubber, and even some metals or alloys, I may embody-into the mounting 10' portion a relatively heavy or large sleeve or bushing 3| made of any material, preferably metallic, suitable for threading to take the stresses imposed by the element 3|; member 34 is internally threaded to coact with the threaded element 3| and its relatively large external surface, of substantial dimension both axially and radially, may be made irregular as indicated at 34 in any suitable way, as by coarse knurling, fluting, threading, or other variations in surface contour whereby it may be interengaged with the material of the mounting portion It, as by moulding the latter thereabout, and thus forming an interlock that is mechanically stronger than would be a direct threaded connection of the element 3| with the mounting portion l6. 1 Such an insert, pref- 'erably having its end face flush with the end slight taper, hardly distinguishable in the drawing, in the mating shapes of the chamber C and the mounting portion it, giving a wedging selfs-eating or self-tightening action under the pressures of grinding, particularly in the forms of Figs. 2, 4, and 5 and tea lesser extent in the form of Fig. 3. Such taper also facilitates dis'-' lodgment under the action of the screw 22. The upper part of the mounting'portion l6, exposed above the face it or the support in, may be crosssectioned to receive a suitable wrench as by providing it with opposed parallel faces 34 and 35 formed by moulding, grinding, milling, or the like;

thereby an. applied wrench may be used to hold the element E of Figs. 4 and 5 against turning while tightening up the tension element 3!, and to turn the element E in Fig. 3 relative to the threaded walls of chamber C, and to aid in loosening up the elements E in all of the illustrative forms when it is desired to remove them from the chamber C of the support iii.

Likewise. many advantages of my invention may be achieved by the use of securing media other than cements such as those above mentioned. For example, where the part of the abrasive element E that enters the chamber C and the annular support it are both of metal suitable to be joined together by any of various solders, solders may be employed and the parts sweated together. In such case, to effect replacement, heat may be applied to weaken the metallurgical junction and the inserted element expelled or forced out of the chamber C by the means above described. In like manner such a junction may be effected as at P, in joining the abrasive portion to and the mounting portion it Where metals are used that are suitable for effecting such junction. 1

It will thus be seen that there has been provided in this invention a disk type of grinding wheel construction in which many thoroughly practical advantages are successfully achieved. The composite elements E, comprising the diamond abrasive portion i5 and the securing porabrasive portion in meeting the particular requirements of any particular grinding operation. For example, for some operations a hard, rigid mounting or support for the active abrasive part may be needed, and in such case the mounting portion i6 may be made of a-suitably hard metal, or by powdered metallurgy, or, by way offurther example, it may be a. ceramically or vitrified bonded structure. For some other grinding operation the active abrading part, such'as the part ii, might need a relatively less rigid or stiff support, and in such case the mounting portion It may be made of a material like natural or synthetic rubber suitably compounded to give the desired hardness, accompanied by such yieldability as may be desired; or other 'resinoids, with appropriate fillers, may be used in making the mounting portion I6 to have a lower modulus of elasticity appropriate to the particular grinding operation to be performed. Thus a wide variety of grinding requirements. can be met in a thoroughly practical way and with greater economy and efllciency than has heretofore been possible. The composite abrasive elements E can be standardized dimensionally for assembly to similarly standardized annular supports i0. thus to facilitate initial making up or assembly of grindin .disks of the desired grinding characteristics, and

the construction facilitates the ready replacement "or substitution,,by the 'user, of the composite abrasive elements. The latter are easily removed from their chambers, even though strong cements or even tight or force fits are employed, and the assembly of new elements to the annular support l easily effected. In this latter connection, where cements, solders, or the like are employed. it is preferred that the lower ends of the mounting portions l8 be chamfered or rounded over, as at 20 in the drawings, thus not only facilitating entry of the mounting portion it into the chamber C, but also to provide an internal space vantages I am enabled to gain without risk of transmits to its abrasive portion IS the share of the total pressure under which the abrasive portion i5 by itself should operate upon the workpiece. With such substantial pressures, the reaction from the plane of grinding upon the exp sed length of the cantilever. mounting portion i6 is one to tend to displace and strain it in a direction transversely of its axis, as well as to put it under compression. The non-abrasive mounting portion l6, according to my invention, can be constructed of materials having structural characteristics uninhibited by the limitations which are imposed if the elements E had to be of the same bonded 'fabrasive structure throughout, and hence I amfenabled to make eflective the diamond abrasive material in that the structures according tomy invention can function undcr stresses of magnitude greater than heretofore possible, As another result also vastly increased grinding capacity is achieved and. aside from making substantial savings in initial cost of manufacture of diamond abrasive disks, lower cost andhigher efficiency of grinding operations are achieved.

Furthermore, tendency toward chattering or like detrimental actions during grinding operations is guarded against in a reliable manner.

' The transverse reactions from the grinding opstraining or distorting the abrasive portion itself."

Each mounting portion l6 serves in effect as a cantilever that takes the stresses from the abrasive portion l5 and in and byitself transmits them to the annular support iii in a way to avoid direct reaction between the abrasive portion i5 and any part of the support l0. Uniformity of mounting and alignment of the abrasive faces i 5 is thereby achievable and maintenance of precision of grinding operation facilitated.

I am thus enabled to bring diamond abrasive materials efllcierltly and inexpensively into operation for surface grinding of large areas of workpieces such as granite, marble, plate glass, and the like; the disk grinding wheel of my invention may be economically constructed and operated in relatively large dimensions and will be seen to be well adapted to withstand the great pressures which have to be employed in such operations; of the total or aggregate pressure with which the rotating structure is pressed against the work, each mounting portion I6 to be understood that all matter hereinabove set forth or shown in the accompanying drawing is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. A grinding wheel construction comprisin an annular support being recessedin a back face thereof to give it substantially a U-shaped crosssection and having a, plurality of chambers of substantial depth and cross-section opening int the front face thereof, said support having a hole leading from the annular recess into the chamber and through the bottomof the latter, a plurality of built-up elements, one for each chamber and each comprising a cantilever mounting portion received and secured in a chamber and carrying an abrasive portion at its outer end, and means coacting with said hole and operable to dislodge the element from its chamber.

2. A grinding wheel construction comprising a rigid annular support having opening into the front face thereof a plurality of chambers having fixed walls of substantial rigidity and giving each chamber substantial cross-section and depth, a plurality of built-up elements, one for each chamber and each comprising a cantilever mounting portion of greater length than the depth of a chamber and received within its chamber and only by the walls of the latter rigidly supported for cantilever action of the portion thereof that projects beyond said front face, said projecting portion carrying at its outer end an abrasive portion of relatively small thickness and comprising bonded diamond grains, said cantilever portion and the wallsof the chamber coacting to prevent 13 material transverse deflection under the transversely directed forces accompanying grinding action by the abrasive portion, the support being recessed at the back face thereof opposite each chamber, there being a hole through the annuiar support from the bottom of each chamber and extending to the recessed back face, and screws extending through the holes and into the recessed back face and each screw being reachabie for turning at said back face and each screw being operable to dislodge the corresponding element from its chamber when desired.

GUNNAR E. HOLLSTROM.

REFERENCE-S, arm! The following references are of record in the file of this patent:

Number Number M UNITED STATES PATENTS Name I Date Strattan et a1 Nov. 12, 1889 Hyde Mar. 30,1915 Hohnhorst Nov. 17, 1931 Hanus Mar. 20, 1931 Van der Pyl Mar. 14, 1939 Benner et a1. Dec. 17, 1940 Milligan et a1 Apr. 28, 1942 FGREIGN PATENTS Gountry Date GreatBritain Mar. 6, 1924 Germany Oct. 23, 1920 Germany July 19, 1924 

